Mu Leonis

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Mu Leonis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Leo
Right ascension 09h 52m 45.81654s[1]
Declination +26° 00′ 25.0319″[1]
Apparent magnitude (V) 3.88[2]
Spectral type K2 IIIb CN1 Ca1[3]
U−B color index +1.38[2]
B−V color index +1.23[2]
Radial velocity (Rv) 14.03±0.19[4] km/s
Proper motion (μ) RA: −217.31[1] mas/yr
Dec.: −54.26[1] mas/yr
Parallax (π) 26.28 ± 0.16[1] mas
Distance 124.1 ± 0.8 ly
(38.1 ± 0.2 pc)
Mass 1.5±0.1[5] M
Radius 14[4] R
Luminosity 63[4] L
Surface gravity (log g) 2.5[4] cgs
Temperature 4,436[4] K
Metallicity [Fe/H] +0.17[4] dex
Rotational velocity (v sin i) 4.5[4] km/s
Age 3.35±0.70[5] Gyr
Other designations
Rasalas, μ Leo, 24 Leo, HD 85503, HIP 48455, HR 3905, SAO 81064.[6]

Mu Leonis (μ Leonis, abbreviated Mu Leo, μ Leo), also named Rasalas,[7] is a star in the constellation of Leo. The apparent visual magnitude of this star is 3.88,[2] which is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 0.02628 arc seconds as measured by the Hipparcos satellite,[1] this system is 124 light-years (38.1 parsecs) from the Sun. In 2014, an exoplanet was discovered to be orbiting the star.


μ Leonis (Latinised to Mu Leonis) is the star's Bayer designation.

It bore the traditional names Rasalas (Ras Elased Borealis) and Alshemali, both abbreviations of Ras al Asad al Shamaliyy,[8] from the Arabic رأس الأسد الشمالي ra’s al-’asad aš-šamālī "the northern (star) of the lion's head". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[9] to catalogue and standardize proper names for stars. The WGSN approved the name Rasalas for this star on 12 September 2016 and it is now so entered in the IAU Catalog of Star Names.[7]


Mu Leonis is an evolved K-type giant star with a stellar classification of K2 IIIb CN1 Ca1.[3] The trailing notation indicates that, for a star of its type, it has stronger than normal absorption lines of cyanogen and calcium in its spectrum.[10] It has around 1.5 times the Sun's mass, but has expanded to around 14 times the Sun's radius. Mu Leonis shines with 63 times the luminosity of the Sun from an outer atmosphere that has an effective temperature of 4,436 K. It is around 3.35 billion years old.[4]

Planetary system[edit]

In 2014 it was announced that Mu Leonis has a planetary companion that is at least 2.4 times as massive as Jupiter and orbits with a period of 358 days. This planet was detected by measuring radial velocity variations caused by gravitational displacement from the orbiting body.[5]

The Mu Leonis system
Companion Mass Semimajor axis
Orbital period Eccentricity Discovery year
b 2.4±0.4 MJ 1.1±0.1 357.8±1.2 days 0.09±0.06 2014


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), Compilation of Eggen's UBV data, transformed to UBV (unpublished), SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b Keenan, P.; McNeil, R. (October 1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245–266, Bibcode:1989ApJS...71..245K, doi:10.1086/191373. 
  4. ^ a b c d e f g h Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209. 
  5. ^ a b c Lee, B.-C.; et al. (2014). "Planetary Companions in K giants β Cancri, μ Leonis, and β Ursae Minoris". Astronomy & Astrophysics. 566: 7. arXiv:1405.2127free to read. Bibcode:2014A&A...566A..67L. doi:10.1051/0004-6361/201322608. A67. 
  6. ^ "mu. Leo -- High proper-motion Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-09-28. 
  7. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  8. ^ Allen, Richard Hinckley (1899), Star-names and Their Meanings, G. E. Stechert, retrieved 2016-09-28. 
  9. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  10. ^ Keenan, Philip C. (August 1987), "Spectral types and their uses", Astronomical Society of the Pacific, Publications, 99: 713−723, Bibcode:1987PASP...99..713K, doi:10.1086/132036. 

External links[edit]

  • Kaler, James B., "Rasalas", Stars, University of Illinois, retrieved 19 August 2014.